Apoptotic cell death is a prominent cellular process associated with vascular remodeling and lesion formation. However, the cellular signals that determine whether cells live or die are poorly characterized. Our preliminary observations indicate that transforming growth factor-beta-1 (TGF-beta-l) exerts cell-specific and diametric effects on the regulation of endothelial cell (EC) versus vascular smooth muscle cell (VSMC) apoptosis. The proposed project will test the hypothesis that the cell-specific effects of TGF-Beta-1 on the regulation of vascular cell apoptosis relates to distinct patterns in ERK vs SAPK (activation coupled to their cross-talk modulation of Smad protein transcriptional activity in EC vs VSMC). We propose a working model in which TGF-Beta-1 stimulates Smad2-Smad4 activity in both EC and VSMC. In EC, this activation is accompanied by increased SAPK activity that in a crosstalk fashion promotes a potentiated activation of Smad2-Smad4 leading to endothelial cell apoptosis. Conversely, our working hypothesis poses that the anti-apoptotic effect of TGF-beta1 in vascular smooth muscle cells involves a co-activation of predominantly ERK signaling that in a crosstalk fashion attenuates the Smad2-Smad4 pro-apoptotic activity. Thus, the proposed project will test the hypothesis that the cell- specific effects of TGF-Beta-1 on vascular cell fate involve differential patterns in the activation of MAP kinases that modulate Smad2-Smad4 transcriptional activity and apoptosis regulation. Specifically we will: Aim I. Define the cell-specific effects of TGF-Beta-1 modulation of ERK vs SAPK activity in association with Smad2-Smad4 activation. Aim II. Define the mediator role of TGF-Beta-1-induced ERK activation in suppressing Smad2-Smad4 pro-apoptotic activity in VSMC. Aim III. Define the mediator role of TGF-Beta-1-induced SAPK activation in promoting Smad2-Smad4 pro-apoptotic activity in endothelial cells. It is anticipated that a comparative analysis between these two vascular cell types will provide further insight into the regulatory mechanisms governing apoptosis as well as the signal transduction apparatus coupled to TGF-Beta-1 receptors in vascular cells and may lead to the identification of novel therapeutic strategies in vascular disease.